Default new users to the Agentic UI and remove its feature flag

[bcotrim]

Related issues

• Fixes STU-2149

How AI was used in this PR

Claude (Opus 5) implemented the change and ran typecheck + unit tests. New-user and existing-user scenarios verified by hand.

Proposed Changes

• New installs open the Agentic UI by default. Existing users stay on classic and opt in via the banner, Settings → Preferences, or the Beta Features menu; everyone can still switch back.
• A one-shot migration decides this per install, keyed on whether the app has launched before. Explicit existing choices (current beta testers included) are left alone, and the persisted default stays false so a failed migration leaves users where they are.
• Removes the enableAgenticUi env flag, keeping the now-empty registry. CLI Tracks events were labelled from that flag rather than the running UI, so classic users were reported as agentic; fixed.
• ⌘/Ctrl+N now falls back to "Add Site…" when agentic chat is off. The menu previously released the key whenever the agentic UI was running, but only the chat composer binds it — so with chat off it did nothing. (Still unbound with chat on while outside a session view; pre-existing and renderer-side.)

Testing Instructions

Back up ~/.studio/*.json; quit Studio between steps.

1. Remove app.json, cli.json, shared.json → Agentic UI, ui_version: 'v2' in the log.
2. Restore, then delete only betaFeatures.enableAgenticUi → classic, with banner + Settings callout.
3. Set it true with lastBumpStats present → agentic; false with lastBumpStats removed → classic. Neither should be rewritten.
4. ⌘/Ctrl+N: New chat in agentic with chat on; Add Site in classic, and in agentic after switching chat off in Settings → AI (no restart needed).

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 5cc4615 vs trunk

app-size

Metric	trunk	5cc4615	Diff	Change
App Size (Mac)	1378.88 MB	1378.86 MB	0.02 MB	⚪ 0.0%

site-editor

Metric	trunk	5cc4615	Diff	Change
load	1069 ms	739 ms	330 ms	🟢 -30.9%

site-startup

Metric	trunk	5cc4615	Diff	Change
siteCreation	6489 ms	6521 ms	+32 ms	⚪ 0.0%
siteStartup	2391 ms	2389 ms	2 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[nightnei]

@bcotrim Everything works great, I just didn't get this point, coudl you please elaborate? Add Site in classic, and in agentic after switching chat off in Settings → AI (no restart needed).

[bcotrim]

@bcotrim Everything works great, I just didn't get this point, coudl you please elaborate? Add Site in classic, and in agentic after switching chat off in Settings → AI (no restart needed).

Part of this PR fixes the ⌘/Ctrl+N shortcut (it was referencing the feature flag).
This point is to confirm that shortcut works to add a new site in classic UI and Agentic UI. Note that in the Agentic UI you need to turn off AI features first otherwise that shortcut will create a new site.

[nightnei]

@bcotrim Everything works great, I just didn't get this point, coudl you please elaborate? Add Site in classic, and in agentic after switching chat off in Settings → AI (no restart needed).

Part of this PR fixes the ⌘/Ctrl+N shortcut (it was referencing the feature flag). This point is to confirm that shortcut works to add a new site in classic UI and Agentic UI. Note that in the Agentic UI you need to turn off AI features first otherwise that shortcut will create a new site.

Thanks for the clarification, it works well 👍